Method for monitoring the cycle of the weft insertion into a weaving machine

ABSTRACT

A method for monitoring the cycle of the weft insertion into a weaving machine. The weft yarn passes a yarn brake and a yarn force sensor and the force acting on the weft yarn is measured in a known fashion and the reaction force of the yarn is converted by a pressure sensitive element into an electrical signal. The electrical signal outputted by the yarn force sensor is electronically amplified in an evaluation unit, is evaluated and is transmitted to an indicator informing the operator of the development of the weft insertion and of disturbances and corrections. For this purpose, the evaluation unit is connected via a data line with a machine control unit. Evaluation unit is supplied with time signals from the machine control unit associated with further machine functions participating at the weft insertion, e.g. the momentary angular position of the main shaft of the machine. The machine control unit receives monitoring signals of the yarn force evaluation via the data line, e.g. for immediate stoppage in case of a yarn breakage occurring during the weft insertion, or to activate a machine related alarm system in case of a disturbance needing the interference by an operator.

FIELD OF THE INVENTION

The invention relates to a method for monitoring the cycle of weftinsertion into a weaving machine with a signal generating sensoractivated by yarn deflection and connected to an evaluation unit.

BACKGROUND OF THE INVENTION

In known weaving machines, the cycle of the weft insertion is determinedby a previously set program and is monitored by yarn feelers ofmechanical, capacitive, tribo-electrical or opto-electrical types. Inorder to assure a reliable response of said sensors to a yarn breakagethe sensors have to react relatively slowly, i.e. by a response timewith a magnitude 10 ms or more. From insertion to insertion in this waythe cycle of the yarn movement during the weft insertion can bedetermined only vaguely by measuring the response points in time ofdifferent sensors provided along the yarn path. A continuous measuringand monitoring of the yarn movement during the weft insertion herewithis excluded. Also an optimization of the cycle of the weft insertion,e.g. by a target control of the air nozzles of the air jet weavingmachine, is impossible in this case. Furthermore, it is difficult todetect problems of a weft insertion early enough. A reliable stop of theweaving machine in case of insertion disturbances, however, is aprerequisite so as to avoid fabric faults. For these reasons theexisting sensors are frequently adjusted so sensitively that they stopthe weaving machine even in a doubtful case. This leads to an increaseddemand for interferences by an operator.

According to the method as known from EP 0 117 571 A for monitoring thefeeding state of a yarn during a weft insertion into a weaving machine,a tuning fork is actuated by the weft yarn which tuning fork duringmovement of the weft yarn transmits oscillations to a sensor providede.g. with piezo-electric material. The movement of the weft yarn isdetected and monitored in order to derive a signal exclusivelyindicating the running movement of the weft yarn. By means of adiagnosis, it is concluded that a yarn breakage has occurred from a yarnstop which occurs at a point in time which would not normally beexpected. The yarn force resulting from the tension in weft yarn is notmeasured. Irrespective of the momentary weft yarn tension, the sensordoes not generate a signal when the weft yarn has stopped.

According to the weft yarn monitoring method known from U.S. Pat. No.3,688,958 A, the sensor provided only generates a signal if the weftyarn is running and even first if the weft yarn has reached apredetermined running speed. The frequency of yarn irregularitiesrubbing at the sensor during the yarn run is measured, but not the yarnforce.

The pulling force in the weft yarn occasionally is measured forscientific purposes in an experimental manner. Sensors used for thispurpose employ strain measuring strips forming mechanical-electricaltransducers. The materials used limit the sensitivity, the capability towithstand overloads, and the limit frequency such that only carefullyprepared laboratory measurements can be carried out for single insertioncycles and only on particularly robust yarns which can stand theadditional load at the deflection points of the sensors. For anindustrial production the measuring method cannot be used, and alsocannot be used because of the limited life duration, the complicatedhandling, and the high costs of those experimental apparatus.

It is an object of the present invention to measure the yarn forceduring a weft insertion with a reasonably priced, robust, accurate andquick-reacting sensor, and to optimize and more reliably monitor thecycle of the weft insertion. The sensor is based on the principle ofyarn deflection. The deflection angle amounts to less than 45°,preferably less than 30°. The limit frequency of the sensor is set above1 kHz, and preferably above 5 kHz. The sensor preferably is realizedwith a piezo-resistive or piezoelectric crystal. For the piezo-resistivemeasuring principle e.g. a force sensor type PK 8870 made by theHoneywell Company is used. The sensor is employed in co-action with adirect voltage amplifier having a limit frequency of at least 1 kHz, andpreferably more than 5 kHz. For carrying out the piezo-electricmeasuring principle e.g. a force sensor of the production program of theKistler Company is employed, in co-action with a charge amplifier. Inthis case, a quasi static output signal is generated by respectivelyresetting the amplifier in the forceless phase of the insertion cycle.Details of the piezo-electrical measuring method are described in detailin the sales documentation of the Kistler Company.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of the measuring arrangement forcarrying out the method according to the invention;

FIG. 2 is a graph illustrating the yarn force signal;

FIG. 3 is a graph similar to FIG. 2 illustrating the yarn force signalwithout any disturbances; and a method for monitoring a weft insertion.

FIG. 4 is a graph illustrating the principles for the optimization ofthe weft insertion.

DETAILED DESCRIPTION

The principle of the measuring arrangement is schematically shown inFIG. 1. A weft yarn feeder 3 withdraws a weft yarn 1 from a bobbin 2.The weft yarn passes through a yarn brake 4 and through a yarn forcesensor 5 according to the invention. The force acting in the weft yarnis measured in known fashion by deflecting the yarn and by convertingthe reaction force 7 of the yarn by a pressure sensitive element 6 intoan electrical signal 13. Further downstream, the weft yarn is passingthe so-called colour selector which is responsible for the operationalco-ordination of different weft yarns for the respective weft insertion.The weft insertion is actively carried out by element 9 whichaccelerates the yarn and drives it further.

The element 9 may be of different design depending on the kind ofweaving machine. It may be a projectile or a gripper or may be the mainnozzle and the subsequent relay nozzles of an air jet weaving machine,or the injector of a water jet weaving machine. During weft insertionthe weft yarn passes through the weaving shed 11 situated betweenscissors 10 and 12. The force measuring element 6 can be mounted to aplate 5 provided with yarn guiding elements or may be integrated intothe yarn path in the machine such that the desired force component isproduced in the force measuring element 6. The element in any case issituated in the yarn path downstream of yarn brake 4, and upstream ofthe entrance of the weaving shed 11; and in the case of air and waterweaving machines upstream of main nozzle 9.

The electric signal 13 output by yarn force sensor 5 is electronicallyamplified in evaluation unit 14, is evaluated and is brought as signal15 into an indicator 16 informing the operator about the cycle of theweft insertion and of disturbances and corrections. For this purpose theevaluation unit 14 is connected via a data line 17 with the control 19of the machine. From control 19 evaluation unit 14 is supplied with timesignals of further machine functions participating at the weftinsertion, e.g. the momentary angular position of the main shaft of themachine. Said machine control also receives monitoring signals of theyarn force evaluation unit 14 via data line 18, e.g. to immediately stopin case of a yarn breakage during the weft insertion or to activate amachine related alarm arrangement in case of a disturbance needinginterference by the operator.

The shape of signal 13 is shown in its timewise development in FIG. 2for the example of an air jet weaving machine. The diagram shows theyarn pull at its vertical axis 20 and time at the horizontal axis 21. Insection 22 outside of the initial weft insertion process there is notension in the yarn. At point in time 23 the yarn is accelerated andenters the weaving shed. This results in a rapid increase of the yarnforce. During time duration 24 the yarn is running through the weavingshed. At point in time 25 the yarn as measured in its length by feederor prewinding device 3 is stopped leading to a typical force peak. Thenthe yarn remains stretched during time duration 26 until at point intime 27 the reed is beating up the yarn against the fabric and is againgenerating a characteristic force peak. Subsequently the yarn is cut atboth sides by scissors 10 and 12. The yarn force drops and the cyclestarts again.

In the following, different possibilities for evaluating the signalswill be described. FIG. 3 shows the force signal for a weft insertionwithout any disturbance analogously to FIG. 2. Monitoring such a signaldevelopment for a predetermined time duration belongs to known prior artof digital signal processing. The signal generated for this purpose bythe sensor in analogous form is digitized in time intervals of a maximumof 10 ms, preferably less than 1 ms, and is compared with limit valuesassociated with the respective time steps. The limit values can be setby the user of the machine on the basis of yarn data or experiencevalues, or may even be determined and set during operation by theevaluation device according to the principle of an adaptive control.Also, a so-called teach-in by the operator is provided. Finally, anaverage value is formed for each time step on the basis of thedetermined cycle of the yarn force learned from operation experience toset a target pattern on the basis of the average values. Each singleweft insertion is compared with the target pattern. As soon as apredetermined tolerance is exceeded an alarm is given or the machine isstopped. A decisive advantage is that the occurred force developmentresulting in a stop subsequently is available for a diagnosis by theoperator and that the force development can be compared with the pictureoffered by the machine itself.

A limit value may be, as shown in FIG. 3, e.g. a maximum pulling force30 during insertion of the yarn. The pulling force is limited to adetermined value due to the simultaneous acceleration of the yarn whichvalue normally is lower than the value occurring when the yarn isstopped. During the entire weft insertion, a minimum yarn force 31 hasto be monitored to immediately detect a yarn breakage. Finally, the peakload of the yarn when stopped at 32 is to be monitored. The magnitude ofthe force peak at the other side is a confirming feature for asuccessfully carried out weft insertion and again is monitored inconnection with a minimum value 32. Also the timewise developments,given by the positions of force peaks 23, 25, and 27, are to bemonitored in an analogous fashion by the control. The function here isnot shown in further detail since it is carried out like the nowadaysconventional monitoring of the arrival of the yarn tip by an opticalsensor at the location of scissors 12 (FIG. 1). FIG. 4 indicates how themethod is used to optimize the weft insertion. The yarn force is shownat the vertical axis 20. Horizontal axis 40 is not to be seen as a timeaxis but is subdivided into sections 41 of the weaving cycle whichsections correspond to a determined number of rotation angle degrees ofthe main shaft of the weaving machine. From this it can be seen howdetermined effects occurring during the weft insertion are associatedwith the control functions of the weaving machine. This is decisive forthe practical operation during optimization of the weft insertion,because the operator has to decide which interferences might be needed,or in an automatic optimization method needed and useful interferenceshave to be displayed for the operator. The correct force development 42is determined numerically by forming average values of a series ofinsertion cycles and is displayed in colours in the screen (in this casedotted). Deviations of particular cycles resulting in a stopping of themachine, like e.g. weft insertions 43 or 44 stopped by yarn breakages,are displayed in a different, clearly visible way. In this case anautomatic force diagnosis also indicates the kind of fault as this isnowadays done in a simple way by alphanumerical displays at the weavingmachines, however, only to a limited extent, e.g. just withdifferentiation between weft faults or warp faults.

In a similar way, the display indicates bad adjustment values, e.g.force peaks 45 which are too high for the yarn stop. Even if in thiscase the machine might not be stopped, the arrow 46 emphasizes thedelicate condition which can be improved by changing an adjustment, e.g.decelerating the weft insertion by lowering the pressure for the relaynozzles.

Although particular preferred embodiments of the invention have beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

What is claimed is:
 1. A method for monitoring the cycle of a weftinsertion into a weaving machine, said method comprising: providing asignal generating piezo-resistive or piezo-electrical yarn force sensorconnected to an evaluation unit; actuating the sensor by deflection witha weft yarn and generating a signal with the sensor; comparing thesignal to a target pattern and deriving at least a diagnosis from thecomparison; continuously measuring the yarn force within the weftinsertion and outside of the weft insertion with the sensor having alimit frequency of at least 1 kHz and with a sampling rate of at least100 Hz with the signal which analogously corresponds to the yarn force;evaluating the signal in a digitized manner in time intervals; andchanging a weaving machine control function adjustment optimizing theweft insertion on the basis of the measured yarn force and/or initiatinga weaving machine control function optimizing the weft insertion on thebasis of the measured yarn force.
 2. The method of claim 1 wherein saidstep of continuously measuring includes measuring the yarn force with apiezo-resistive crystal in connection with a direct voltage amplifierhaving a limit frequency of at least 1 kHz.
 3. The method of claim 1wherein said step of continuously measuring includes measuring the yarnforce with a piezo-resistive crystal in connection with a direct voltageamplifier having a limit frequency of more than 5 kHz.
 4. The method ofclaim 1 wherein said step of continuously measuring includes measuringthe yarn force with a piezo-electrical crystal in connection with acharge amplifier.
 5. The method of claim 1 including evaluating thesignal in relation to rotation angle positions of a main shaft of theweaving machine associated with predetermined portions of a weavingcycle.
 6. The method of claim 1 including monitoring the yarn force inview of a minimum limit value in predetermined portions of a weavingcycle related to time or to a rotation angle of a main shaft of theweaving machine, and initiating a predetermined function of the weavingmachine if the yarn force drops below the minimum limit value.
 7. Themethod of claim 1 including monitoring the yarn force in view of amaximum limit value during a predetermined portion of a weaving cyclerelated to time or to a rotation angle of a main shaft of the weavingmachine, and initiating a predetermined function of the weaving machineif the yarn force exceeds the maximum limit value.
 8. The method ofclaim 1 including monitoring a magnitude of predetermined force peaks ofthe yarn force during a weft insertion cycle with predeterminedtolerance fields related to time or to a rotation angle of a main shaftof the weaving machine, and initiating a predetermined function of theweaving machine if the magnitude is outside the tolerance field.
 9. Themethod of claim 1 including forming a target pattern picture based uponthe development of the yarn force during a selected phase of the weftinsertion, monitoring the yarn force in view of maintaining the targetpattern picture, and initiating a predetermined function of the weavingmachine in the event of a deviation from the target pattern picture.